Microbial associates of an endemic Mediterranean seagrass enhance the access of the host and the surrounding seawater to inorganic nitrogen under ocean acidification

• Published in: Scientific Reports
• Main Authors: Pfister, Catherine, A, Cardini, Ulisse, Mirasole, Alice, Montilla, Luis, M, Veseli, Iva, Gattuso, Jean-Pierre, Teixido, Nuria
• Other Authors: Stazione Zoologica Anton Dohrn (SZN), Laboratoire d'océanographie de Villefranche (LOV), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de la Mer de Villefranche (IMEV), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institute for Sustainable Development and International Relations, Sciences Po (Sciences Po)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: [SDE.BE]Environmental Sciences/Biodiversity and Ecology; Ocean acidification
• Online Access: https://hal.science/hal-04308981; https://hal.science/hal-04308981/document; https://hal.science/hal-04308981/file/Pfisteretal%202023%20Microbial%20associates%20Posidonia%20Ischia%20Scie%20Reports.pdf; https://doi.org/10.1038/s41598-023-47126-4

Seagrasses are important primary producers in oceans worldwide. They live in shallow coastal waters that are experiencing carbon dioxide enrichment and ocean acidification. Posidonia oceanica, an endemic seagrass species that dominates the Mediterranean Sea, achieves high abundances in seawater with relatively low concentrations of dissolved inorganic nitrogen. Here we tested whether microbial metabolisms associated with P. oceanica and surrounding seawater enhance seagrass access to nitrogen. Using stable isotope enrichments of intact seagrass with amino acids, we showed that ammonification by free-living and seagrass-associated microbes produce ammonium that is likely used by seagrass and surrounding particulate organic matter. Metagenomic analysis of the epiphytic biofilm on the blades and rhizomes support the ubiquity of microbial ammonification genes in this system. Further, we leveraged the presence of natural carbon dioxide vents and show that the presence of P. oceanica enhanced the uptake of nitrogen by water column particulate organic matter, increasing carbon fixation by a factor of 8.6-17.4 with the greatest effect at CO 2 vent sites. However, microbial ammonification was reduced at lower pH, suggesting that future ocean climate change will compromise this microbial process. Thus, the seagrass holobiont enhances water column productivity, even in the context of ocean acidification.